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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
2*x-(8/x) = 0
2*x-8*x^-1 = 0
2*x^1-8*x^-1 = 0
(2*x^2-8*x^0)/(x^1) = 0 // * x^2
x^1*(2*x^2-8*x^0) = 0
x^1
2*x^2-8 = 0
2*x^2-8 = 0
DELTA = 0^2-(-8*2*4)
DELTA = 64
DELTA > 0
x = (64^(1/2)+0)/(2*2) or x = (0-64^(1/2))/(2*2)
x = 2 or x = -2
x in { -2, 2}
x in { -2, 2 }
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